I recently did an immersion brew at 21% brew ratio. Just under half the water was retained in the grounds. The standard way of calculating extraction is just solids in the cup divided by initial coffee and this resulted in a value of 12.3%. This was a hot brew that was left on the grounds for many hours and it sure didn't taste underextracted.

But suppose all of the liquid in the grounds was included in the calculation?Then the extraction would be given by:

I don't know if you remember in the old Aeropress thread where Alan Adler was doing what we're talking about. AndyS reprimanded him for using a non-standard extraction value in order to fluff up his results. I always thought that was an interesting exchange. We use the idea of extraction in two ways.

If you brew perfect coffee but spill half of it does the extraction go down by 50%?

In one sense it does, but the balance of extracted components doesn't change. The problem is that we use extraction as a proxy for this balance since we have no other simple means for measuring it (other than our senses). So the two ideas, one about economics and the other about balance, are conflated.

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